The present invention relates to cooking ovens, and in particular, to combination ovens and steamers.
Combination ovens provide the ability to cook foods using steam, hot air or a combination of both. A motor driven fan is used to circulate air within a cooking chamber past electrical heating elements or gas fired heat exchange tubes. Combination ovens can be designed with or without a boiler. To produce steam within the cooking chamber, a water line feeds water into the cooking chamber near the heating elements to vaporize the water.
It is well known that the rate of thermal heat transfer increases in proportion to the surface over which the heating occurs. Thus, combination ovens typically feed the water within the inner diameter of the fan so that the water is drawn through the fan. Contact of the water with the fan blades separates the water into small droplets having an effective large surface area which can be vaporized more efficiently. To further improve thermal efficiency, some prior art combination ovens include an atomization element at the hub of the fan which is rotated by the motor. The atomization element which acts to break up the water before it is further reduced by the fan blades. This two stage atomization process produces a fine mist of water surrounding the heating elements.
One type of two stage atomizer is disclosed in U.S. Pat. No. 5,014,679, wherein the atomizer element is a cylindrical drum forming a trough with an open end into which the water is fed. As the drum is rotated, centrifugal force directs the water to pass through the open end where it is broken up by shear forces at the circular edge. The broken up water is then directed radially outward to a fan. A variation on this design includes a perforated cylindrical drum with centrifugal force directing the water out of the perforations. The water is broken up more finely in this design due to increased shearing of the water by the perforations.
An alternative design is disclosed in U.S. Pat. No. 5,530,223. This patent discloses a combination oven in which the water is directed at an outer surface of a pre-atomizer as it is rotated. The pre-atomizer is a sphere, a hemisphere or a plate having no openings. The contact of the water with the outer surface of the rotating atomizer element preliminarily breaks up the water before it is drawn into the fan. However, in this design, there is relatively little shear forces acting on the impinging water, compared to the perforated drum, such that the water is not as finely broken up.
Accordingly, a combination steam and convection oven is desired that provides improved atomization of water.